Fuel Issue. Carb?

[gable74]

72 K20
stock 350 internals
HEI
Electric fuel pump
Edelbrock 1400 carb

Truck sits a bit but usually has no issues. Last week I loaded her up to take a trip to the dump and as soon as I put it in gear it bogged down and ran like crap. Idles fine and revs fine in park/neutral.

I went for the easy stuff first.

Changed the plugs and wires (they were due anyway), and both looked fine.
Changed the fuel filter.
Checked vacuum - 18" once it was warmed up.
Timing was fine
Fuel pressure at the carb was about 5psi, maybe a hair less.

While doing some testing I found something interesting. If I turned the key on (don't start it) and let the fuel pump run for about 60 seconds, the truck would start and run perfect, drive perfect, and felt like normal. After about 30 sec it would fall on its face again and bog down in gear. I can do this repeatedly with the same results. I could replace the fuel pump and regulator (or install a stock mechanical pump) in case they aren't keeping up under a load, but I got a feeling its in the carb. Looking for second opinions.

Thanks,

[Sheepdip]

Fuel Pump.
I went thru the same issue/symptoms awhile back, determined it was the fuel pump giving up the ghost, and it did before I could get it changed about 2 miles from the house so I got to use my AAA card.

[gable74]

Originally Posted by Sheepdip

Fuel Pump.
I went thru the same issue/symptoms awhile back, determined it was the fuel pump giving up the ghost, and it did before I could get it changed about 2 miles from the house so I got to use my AAA card.

Copy that. I planned on putting a mechanical back in if it was the pump, so I will start there. Thanks!

[gable74]

Swapped out the electric fuel pump and regulator for a stock Delphi mechanical pump. Engine still doing the same thing. Bogging down bad in gear. I'm stumped.

[Myself]

Sometimes a weak spark will ACT like a fuel issue and have you chasing your tail. Have you checked for a bad distributor cap? coil? module?

[Wrenchbender Ret]

The sock on the fuel inlet in the tank is plugged up. Another possibility is there could be a fuel filter under the cab along the frame a po put in that you don't know about.

George

[Steeveedee]

How many miles on the previous plugs and wires? HEI rotors will burn through with high mileage and cause similar symptoms. Easy to check- just pull the rotor and pour a little gas in the well at the center (if there is any discoloration). It'll weep right through a burn-through. Sometimes, you can see right through the rotor.

[bowtie72]

Check your fuel flow. Take the line off before the regulator and check flow. If good try the flow after the regulator. The rubber could have deteriorated and not allowing flow. This gas these days is horrible.

[gable74]

Originally Posted by Myself

Sometimes a weak spark will ACT like a fuel issue and have you chasing your tail. Have you checked for a bad distributor cap? coil? module?

Originally Posted by Steeveedee

How many miles on the previous plugs and wires? HEI rotors will burn through with high mileage and cause similar symptoms. Easy to check- just pull the rotor and pour a little gas in the well at the center (if there is any discoloration). It'll weep right through a burn-through. Sometimes, you can see right through the rotor.

Originally Posted by Wrenchbender Ret

The sock on the fuel inlet in the tank is plugged up. Another possibility is there could be a fuel filter under the cab along the frame a po put in that you don't know about.

George

Originally Posted by bowtie72

Check your fuel flow. Take the line off before the regulator and check flow. If good try the flow after the regulator. The rubber could have deteriorated and not allowing flow. This gas these days is horrible.

Its an HEI distributor, and my next step is to inspect/replace the cap/rotor. If that doesn't do it, I am going to set up a temp fuel cell in the bed and run a hose to the pump. Removed the regulator when I installed the mechanical pump. Plugs are brand new, just replaced them, and I replaced the filter on the frame rail. I really thought it was a fuel issue, but unless there is a clog in the line, I have exhausted all those possibilities.

[HotWheelsFan]

Sounds like fuel delivery is not adequate at times.

With new pump, check the rest of the fuel system. I have seen new fuel hoses deteriorate on the inside, debris in metal fuel lines, tee's, and tanks.

Might as well make sure no clogs in carb such as in-carb filter, float/ needle and seat in working order and no debris clogging main jets.

And yes to double checking primary electrical ignition and spark output under load.


Intermittent problems can be a pain sometimes, it can include items that are uncommonly looked at or the smallest little thing acting up at certain times.

Bob

[Myself]

The reason I suggested weak spark is I've had it happen a couple times through the years....and BOTH times I thought it was fuel related. Once I had the hei coil go bad. I was young, talked to an older guy and he said ohm it out. It didn't read out on the secondary side so I swapped it out with a stocker off an old engine and it ran fine. Next time I thought I had crap in the carb or a bad needle or something. I'd just run a few miles towards work and it would just start running like poo-poo. After checking out the fuel system I swapped in another distributor and problem solved. Then I started swapping out parts one at a time to figure out EXACTLY what crapped in that Hei.....it was the condenser! First and only time I'd ever had one go bad.

[rockyrivermark]

There’s an old saying “90% of carb problems are ignition”